Grinding machine

ABSTRACT

A grinding machine for grinding a workpiece having a plurality of portions thereon to be ground is provided having a first stop member for limiting the advancement of a grinding wheel head during rough grinding operations, a second stop member for limiting the advancement of the grinding wheel head during fine grinding operations, and a third stop member for limiting the retraction of the grinding wheel head during fine grinding operations to a point near the advancement limit thereof during the rough grinding operations. The machine is operative to successively roughly grind all of the plurality of portions of the workpiece, then to successively fine grind all of the roughly ground portions.

United States Patent Oishi [s41 GRINDING MACHINE 3,683,558 51 Aug. 15, 1972 72 I t K buro hi K J l 1 nve n or em ois anya apan Przmary Exanuner-Harold D. Whitehead [73] Asslgneei Toyoda Koki Kllbll-Shiki Attorney-Oblon, Fisher&Spivak Aichi-ken, Japan 221 Filed: March 26, 1971 [571 v ABSTRACT A grinding machine for grinding a workpiece having a [21] P 128386 plurality of portions thereon to be ground is provided having a first stop member for limiting the advance- [30] Foreign Application Priority Data ment of a grinding wheel head during rough grinding operations, a second stop member for limiting the ad- March 28, 1970 Japan ..45/2624l vancemem of the grinding wheel head during fine grinding operations, and a third stop member for limit- (g1. ..5l/l01 R, ing the retraction of he grinding wheel head during 1 fine grinding operations to a point near the advance [58] [held of Search 1/101 R, 165.78, 165.79 ment limit thereof during the rough grinding opera tions. The machine is operative to successively I Reerences Cited roughly grind all of the plurality of portions of the UNITED STATES PATENTS 4 workpiece, then to successively fine grind all of the r und rtions. 2,101,796 12/1937 Green ..'....51/l65.78 x gm 2,460,737 2/1949 Flygare ..51/l65.78 X 16 Claims, 11 Drawing Figures l g I /,6 I4 L k 1., y \l i I3 9 v 4 T*'C' l 1 Qt 1 wt n w-,2" I X W 94 32\ ,4 it I: 7 Y :fz If 20 73 F ""52. 1/0 #2 0r f 2 3 o l L I 2 24 a 90 Patented Aug. 15, 1972 5 Sheets-Sheet 1 t 5 My k N N. E mm INVENTOR KENZABURO OlSHl BY (966M, 531., JpJmc ATTORN EYS Patented Aug. 15, 1972 3,683,558

5 Sheets-Sheet 2 Patented Aug. 15, 1972 5 Sheets-Sheet 4 uwq E v Qt w g g g Q 5 Patented. Aug. 15, 1972 5 Sheets-Sheet 5 GRINDING MACHINE BACKGROUND OF THE INVENTION The present invention relates to a grinding machine in which rough and fine grinding operations are successively performed on a workpiece having a plurality of portions to be ground.

Heretofore, a workpiece having a plurality of working portions thereon, such as a camshaft for a vehicle, has always been worked by two processes. In a first of such processes, the workpiece has been rough worked by a turning machine and, in the second process, the workpiece has been fine ground by a grinding machine, such as a cam grinding machine, for obtaining the desired final dimension thereof. However, as the automobile industries have been developed in recent years, improved working processes for such workpieces have also been developed, consequently a grinding operation is now directly applied to an unworked workpiece, namely on the forged or casted workpiece per se without an initial turning process. As such, the unworked workpiece normally has such a large amount to be removed therefrom, such as 3 to mm. on its diameter, that it is impossible to perform both rough and fine grinding operations on the workpiece with a single grinding machine, taking into consideration the maintenance of working accuracy as affected by roundness, roughness, and the like of the workpiece. Thus, the workpieces have had to be ground by two separate processes using two grinding machines, in which one of the grinding machines has been employed for carrying out a rough grinding operation and the other grinding machine performs a fine grinding operation.

On the other hand, although a single grinding machine has more recently been employed for carrying out both rough and fine grinding operations, in such grinding machines, only one of the portions on the workpiece being ground is rough ground and thereafter successively fine ground, and subsequently the next workpiece portion is successively rough and fine ground, and in such a manner all of the grinding portions are eventually finished. In such processes, a dressing operation is required during each grinding cycle, namely at the completion of each rough grinding operation. Accordingly, it should be understood that presently many dressing operations are required for completing a single workpiece, and consequently this causes the working time to be increased and the grinding efficiency to be decreased.

SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide a new and improved unique grinding machine in which all of the portions to be ground on the workpiece are first successively rough ground and thereafter successively fine ground.

Another object of the present invention is to provide a grinding machine for grinding a plurality of portions on a workpiece having improved efficiency through the elimination of idle grinding time normally characteristic of such machines.

A further object of the present invention is to provide a grinding machine for grinding a workpiece having a plurality of portions thereon to be ground which is fast and efficient and provides improved working accuracy.

A still further object of the present invention is to provide an improved cam grinding machine wherein the contact force between a cam roller and a master cam is easily changed.

Briefly, in accordance with this invention, the foregoing and other objects are, in one aspect, attained by the provision of a grinding machine for grinding a workpiece having a plurality of working portions wherein after all the working portions are rough ground, fine grinding operations are subsequently and successively conducted on the rough ground portions. A first stop member is provided for limiting the advancement of the grinding wheel head during rough grinding operations and a second stop member is provided for limiting the advancement of the grinding wheel head during fine finishing operations. In addition, a third stop member eliminates idle grinding time by limiting the retraction of the grinding wheel head to a point near the advancement thereof during the rough grinding operations.

BRIEF DESCRIPTION OF THE DRAWINGS another embodiment of a portion indicated by the letter A in FIG. 2;

FIG. 4 is a sectional view taken along the line IV-IV of FIG. 2;

FIG. 5 is a sectional view of a tail stock mounted on the grinding machine;

FIG. 6 is a sectional view taken along the line VI-VI of FIG. 5;

FIG. 7 is a detailed sectional view of a feed mechanism of the grinding machine;

FIG. 8 is a sectional view taken along the line VIII- VIII of FIG. 1;

FIG. 9 is an enlarged sectional view taken along the line IX-IX of FIG. 1;

FIG. 10 is an elongated sectional view taken along the line XX of FIG. 8; and,

FIG. 11 is a hydraulic circuit showing a compensating device used in the grinding machine of this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Now, with reference to the accompanying drawings, and more particularly to FIG. 1 thereof, there is shown a cam grinding machine constructed according to the present invention which comprises a bed 10 having a grinding wheel head 11 slidably mounted thereon. A grinding wheel spindle 12a is rotatably joumalled on the grinding wheel head 11 and has a conventional grinding wheel 12 positioned at one end thereof and a pulley 15 at the other end. A driving motor 13 for driving the grinding wheel 12 is mounted on the rear of the grinding wheel head 11. The pulley on the grinding wheel spindle 12a and another pulley 14 keyed to a drive shaft of the motor 13 are operatively connected by a V-belt 16, whereby the motor 13 drives the grinding wheel 12 through the pulleys 14 and 15 and the V- belt 16.

A hydraulic actuator for rapid feed movement of the grinding wheel head 11, generally indicated by the reference numeral 21a, is mounted on the bed 10 and comprises a cylinder 21 and a piston 22 slidably mounted therein. A feed screw shaft generally indicated by the reference numeral a rotatably but not axially movably perforates the piston 22. A threaded portion 20 integrally formed on the feed screw shaft 20a is engaged with a threaded block 18a which is secured to the lower side of the grinding wheel head 1 1 and with another threaded block 18 which is also mounted on the lower side of the grinding wheel head 11 for slight axial movement relative thereto. A compression spring 17 is inserted between the threaded blocks 18 and 18a and surrounds the threaded portion 20 of the feed screw shaft 20a for eliminating any backlash that might occur therebetween. A stop plate 19 is provided on the bed 10 for restricting advancement of the end of the feed screw shaft 20a or the grinding wheel head 11 during rapid feed movement thereof. At the right end of the feed screw shaft 20a there is provided a gear 23 which is operatively engaged with a gear 25 through a counter gear 26 rotatably mounted on the bed 10. The gear 25 is keyed to a driving shaft 24 which is operatively connected with a grinding infeed device for the grinding wheel head 11, presently to be described.

A pair of slide ways 27 are formed on the front, or left hand side, as viewed in FIG. 1, of the bed 10 perpendicular to the slide way of the grinding wheel head 11 for slidably mounting a traverse table 28 thereon. A swing table 32 is swingably mounted on the traverse table 28 and has a spindle 30 and a tail stock 70 thereon, which are shown in FIGS. 2 and 5 in detail, for rotatably supporting a workpiece W, such as, for example, a cam shaft, therebetween. The spindle 30 is rotatably mounted on the swing table 32 by means of bearing members 33 and 34 and has a plurality of master cams 35 on the intermediate portion thereof, as shown in FIG. 2. The master cams 35 have a form corresponding to the shape of cams to be generated on the workpiece W. A brake device 36 is provided on the left end of the spindle 30 for controlling the rotational speed thereof in a well known manner. The spindle 30 is connected through universal joints 37 and 38 to a drive shaft 39 of a conventional reduction gear device, not shown, which is connected to a drive motor, not shown.

Next, referring to FIG. 4, a cam roller 41 is rotatably mounted on a supporting member slidably mounted on a frame 43 and adapted to be movable in a parallel path relative to the axis of the spindle 30. The frame 43 is secured to the rear end of a head stock 42 which is mounted on the traverse table 28. A rack 44 fixed on the lower side of the supporting member 40 is operatively connected to a star gear 47 through a gear 45 rotatably supported by the frame 43 and a gear 48 fixed to another shaft whichis rotatably journalled on the frame 43 and has the star gear 47 at the other end thereof. The star gear 47 engages dogs 49 mounted on a dog bar 48a secured on the bed 10 and arranged at predetermined spaced intervals corresponding to the cam intervals on the workpiece W. The star gear 47 is advanced one by one of its teeth by the engaging dogs 49 when the traverse table 28 on the bed 10 is indexed longitudinally so as to index one of the cams to be ground on the workpiece W with respect to the grinding wheel 12. Thus, the supporting member 40 is shifted by one pitch of the star gear 47 through the gears 48 and 45 and the rack 44, so that the cam roller 41 is shifted to the adjacent master cam from the previously used one.

In a device for urging the master cams 35 toward the cam roller 41, one end of each of a pair of springs 50 is fixed to a shaft member 51 supported by spaced arm members 52, 52 and an intermediate arm 52a secured to the front side of the swing table 32, as shown in FIGS. 2 and 4, while the opposite ends of the springs 50 are connected to respective threaded sleeves 54 which may be axially moved by turning adjusting nuts 53 and are prevented from rotating by keying pins 55. Thus, the master cams 35 on the swing table 32 are urged toward the cam roller 41 by the tension of the springs 50. This urging force may be changed by changing the tensions of springs 50, and it may be realized by turning the adjusting nuts 53. FIG. 3 shows another embodiment of the device for urging the master cams 35 toward the cam roller 41. In FIG. 3, the upper end of the spring 50 is secured to a threaded sleeve 62 which is threadedly received in a piston member 61. The piston 61 is slidably mounted in a cylinder 60 secured on the upper portion of the head stock 42. When pressure fluid is supplied from a conventional pressure source, not shown, to the lower chamber of cylinder 60, the spring 50 which is indirectly connected to the piston 61 through the threaded sleeve 62 is upwardly extended to intensify the force of the spring 50, or in other words, the contact force between the cam roller 41 and the master cams 35 may be automatically changed in accordance with the grinding condition by means of the supply of pressure fluid into the lower or upper chambers of the cylinder 60. Therefore, it should be understood that, for example, a strong contact force may be applied against the cam roller 41 during a rough grinding process in which a large amount of grinding resistance may be generated between the workpiece W and the grinding wheel 12, while on the other hand, during a fine grinding process, in which a relatively smaller grinding resistance only need be generated between the workpiece W and the grinding wheel 12, a relatively weaker contact force may be applied against the cam roller 41 to avoid deformation of the elements of the machine tool, such as the grinding wheel spindle 12a and the like or the workpiece W.

The threaded sleeve 62 may be axially moved by turning the piston 61, which may be achieved by inserting a slender bar or the like into a hole 61b drilled in the upper portion 61a of the piston 61, the sleeve 62 being prevented from rotating by a pin 63 secured on the head stock 42. Accordingly, the tension force of the spring 50 in its initial condition may be changed by turning the piston 61, thereby causing the contact force being exerted by the master cams 35 against the cam roller 41 to change.

A cylinder 65 is formed on the front side of the head stock 42, as shown in FIG. 4, and arranged between the vertically oriented springs 50, as indicated by the dotted lines in FIG. 2. In FIG. 4, a piston 66 is slidably mounted in the cylinder 65, a piston rod 67 thereon extends downwardly to abut a roller 68 rotatably mounted on the right end of the arm member 52a. Thus, the arm member 52a is urged downwardly by the downward movement of piston 66 to release the engagement between the cam roller 41 and the master cams 35, as shown by the solid line in FIG. 4, so as to avoid collision between the master earns 35 and the cam roller 41, and thus, in this fashion, the cam roller 41 may be shifted from the previously used master cam to another one, or the workpiece W may be unloaded from or loaded on the grinding machine. Upon the upward movement of the piston 66, the swing table 32 swings toward the cam roller 41 so that one of the master cams 35 comes into contact therewith, whereby the next grinding operation may be practiced.

The upward movement of the piston 66 is made so rapidly that a throttle valve 69 is built in the upper portion of the piston 66 for restricting fluid flow from the upper chamber of the cylinder 65 at the near end of the upper stroke end of the piston 66. Consequently, upward speed of the piston 66 is decreased for the purpose of avoiding an abrupt abutment of the master earns 35 with the cam roller 41, so that damage of the master earns 35 is precluded.

A hydraulic actuator 29 mounted in the bed is operatively connected with the traverse table 28 having the swing table 32 and the head stock 42 thereon for transversely reciprocating the traverse table 28 along slide ways 27, as shown in FIG. 1. An index plate 28a having a plurality of predetermined spaced notches thereon, not shown, is attached on the front side of the traverse table 28. An engaging pin, not shown, is pro vided on the front side of the bed 10 for engaging the spaced notches of the index plate 28a by means of a conventional indexing means. As the spaced notches are formed at the same intervals as the cams on the cam shaft, one of the cams to be ground is indexed against the grinding wheel 12 upon engagement of the engaging pin and one of the notches on the index plate 28a.

The tail stock 70 is mounted on the swing table 32 through a stationary base 87 at the opposite side of the spindle 30 for rotatably supporting the workpiece W, as shown in FIGS. 5 and 6 in detail. Referring to FIG. 5, a telescoping sleeve 73 for receiving a work center 72 is slidably mounted in a tail stock body 71 secured on the swing table 32. The projection of the work center 72 is effected by a spring 74 which is inserted between the right end of the sleeve 73 and an adjusting screw 77. The adjusting screw 77 is threadedly engaged with a piston 76 which is slidably received in a cylinder 75 attached to the right end of the tail stock body 71, and serves to vary the force of the spring 74 by turning a knob 78 integrally formed on the outer end of the adjusting screw 77. Moreover, the compression of the spring 74 or the compression of the work center 72 against the workpiece W may be automatically changed by controlling the supply of pressure fluid into the left or right chambers of the cylinder 75. Accordingly, the compression of the work center 72 is automatically and simultaneously changed when a rough grinding operation is changed to a fine grinding operation in a well-known manner. It should be understood that, during rough grinding, the grinding wheel head 11 is fed at a high speed rate, such as 10 mm./min., and thus the compression of the work center 72 must be increased for preventing any pushing back thereof caused by the grinding resistance. On the other hand, during a fine grinding operation, when the grinding wheel head 11 is fed at relatively slower speed and the grinding resistance is accordingly decreased, the compression of the work center 72 may be decreased. In other words, in case of intensive compression of work center 72, the workpiece W is strained and begins to whirl by the deflection thereof, which is undesirable for maintaining proper working accuracy.

On the inner end of the sleeve 73, there is integrally formed a piston 86 which is slidably mounted in a cylinder formed in the tail stock body 71. Therefore, the work center 72 may be automatically advanced and retracted from the workpiece W by controlling the supply of pressure fluid into the left chamber of the cylinder 85 or exhausting the same therefrom. Moreover, the sleeve 73 is prevented from rotating a pin 79 threaded in the tail stock body 71, as shown in FIG. 6, and is partially provided with a rack 73a on the opposite side thereof from the pin 79. The rack 73a is meshed with a pinion 82 integrally formed on a vertical shaft 81 rotatably mounted in the tail stock body 71. A lever 80 is connected with the vertical shaft 81, whereby the work center 72 may be manually reciprocated against the workpiece W by operating the lever 80.

The tail stock body 71 is adapted to be slidable on the stationary base 87 in s direction perpendicular to the axis of the work center 72 and may be secured thereon by conventional fixing means, such as bolts, not shown. Adjusting bolts 88 are threadedly engaged with the tail stock body 71 for modifying the tapered portion produced on the workpiece W or for adjusting the relative position of the work center 72 with respect to the spindle 30.

On the rear end of the grinding wheel head 11, there is provided a dressing device 90, as shown in FIG. 1. A sleeve 93 is mounted in a dressing housing 91 and has a diamond dresser 92 at the forward end thereof facing the grinding wheel 12. On the other end of the sleeve 93, there is provided a well-known infeed device 94 for intermittently infeeding the dresser 92 toward the grinding wheel 12. The infeed device 94 is cooperative with a known compensator 98 connected with the right end of the driving shaft 24 for compensating the wear of the grinding wheel 12. When a dressing operation is completed after infeeding the diamond dresser 92, the grinding wheel head 11 is moved toward the grinding wheel l2the same amount as the infeed of the dresser 92, whereby the relative position of the grinding wheel 12 with respect to the workpiece W is compensated for wear of the grinding wheel and dressing thereof. The dressing housing 91 is slidably mounted on a slide base 95 mounted on the grinding wheel head for movement in a path parallel with the axis of the grinding wheel 12 and is operatively connected to a hydraulic actuator 96 for reciprocatively moving the dressing device 90, whereby the grinding wheel 12 may be dressed. In such dressing operations for the grinding wheel 12, it is preferably better to change a dressing condition according to whether rough or fine grinding operations are being preferred. Thus, the dressing speed for rough grinding may be relatively faster to sharpen the grinding wheel 12 for improving the efficiency of the grinding operation. On the other hand, the dressing speed for fine grinding may be slow to produce the relative flat surface on the grinding wheel 12 for maintaining a high degree of accuracy, such as roughness, roundness and the like, on the workpiece W. Means for changing the dressing condition may be realized in a conventional manner, for example, by restricting the fluid flow into the hydraulic actuator 96 by a throttling means.

Next, the infeed device for the grinding wheel head 11 will be explained, with reference to FIGS. 7, 8, 9 and 10. a

In FIG. 7, the driving shaft 24 projects from the front side of the bed and has a hand wheel 110 keyed to the forward end thereof. A bushing member 101 is concentrically disposed thereon, being secured to the front side of the bed 10. A cylindrical member 102 is rotatably mounted in the bushing member 101 and also is adapted to be rotatable with respect to the driving shaft 24 which is concentrically received therein. On the right end of the cylindrical member 102 there is provided a pinion 103 which is meshed with a rack 123 of a feed device 120, presently to be described. A flange 105 having a projection 104 thereon is integrally formed on the intermediate portion of the cylindrical member 102. A cylindrical bore 106 formed in the forward end of the cylindrical member 102 receives a slidable piston 108 for axial movement therein, but it is prevented from rotating by a key 107. A tapered contact surface 108a is formed on the left side of the piston 108 for frictional engagement with a mating tapered contact surface 111a formed on a clutch member 11] which is secured to the hand wheel 110. When the piston 108 is moved to the left by the supply of pressure fluid from a pressure source, not shown, to a right chamber 109 of the cylindrical bore 106 through a port 116 and a fluid passage 115, the tapered contact surfaces 108a and 111a are brought into frictional engagement with each other. However, when pressure fluid is not supplied to the right chamber 109, the tapered contact surfaces 108a and 111a may be disengaged by a spring 117 inserted therebetween. Consequently, the grinding wheel head 11 is automatically fed toward the workpiece W by the feed device 120 when the frictional contact surfaces 108a and 1 1 1a are brought into engagement with each other, and on the other hand, when the frictional contact surfaces 108a and 111a are disengaged, the grinding wheel head 11 may be manually moved toward and away from the workpiece W by operation of the hand wheel 110 or adjusted to a desired position relative to the workpiece W. An adjusting ring 112 is fixedly mounted on the cylindrical member 102 by a set bolt 113 threadedly mounted in the adjusting ring 112 and has an engaging pin 114 thereon for engaging a stop member, not shown, provided on the bed 10. It limits the extent to which the grinding wheel head 1 1 may be retracted. The engaging portion between the stop member and the engaging pin 114 may be adjusted by loosening the set bolt 1 l3, and thus the grinding wheel head 11 may be retracted to a desired position.

Along the rotating path of the projection 104 of the flange 105, there is provided a first stop member for limiting the advancement of the grinding wheel head 11 during rough grinding operations and a second stop member for limiting the advancement of the grinding wheel head 11 during fine grinding operations, which will be described hereinafter. Referring to FIGS. 7 and 8, the first stop member 130 comprising a cylinder 132 and a piston 133 is mounted on a sectorshaped member 131. A piston rod 134 of the piston 133 functions as a stop member when the piston 133 is leftwardly disposed, as viewed in FIG. 7, under the force of pressure fluid being supplied from a conventional fluid source P through a change-over valve 136. The sector-shaped member 131 is adjustably mounted on the front side of the bed 10 by pins 135 and corresponding elongate slots 131a formed therein for changing the relative position of the first stop member 130 with respect to the projection 104. It should be understood that the relative position of the first stop member 130 may be changed according to the variation of the amount desired to be removed from the workpiece W.

The second stop member 104 is mounted on the bed 10 adjacent to the first stop member 130 and comprises a plunger 142 slidably received in a supporting block 141 secured to the bed 10. An inclined flat surface 142a is formed on the top end of the plunger 142 for engaging with the projection 104, and a spring 143 is inserted between the plunger 142 and the supporting block 141 to normally urge the plunger 142 away from an engagement position with respect to the projection 104. A longitudinally extending slot 145 is formed on the outer periphery of the plunger 142 and is operatively engaged with a pin 146 threadedly engaged with the supporting block 141 to prevent rotation of the plunger 142 therein. A shaft is rotatably mounted in the supporting block 141 and has a threaded portion 144 at one end thereof and a pinion 147 at the other end. The threaded portion 144 is threadedly engaged with the plunger 142 for upwardly or downwardly moving the plunger 142, as viewed in FIG. 8, responsive to the rotation of the shaft. The pinion 147 is meshed with a rack 153 which is partially formed on a piston rod 152 of a piston 151. The piston 151 is slidably received in a cylinder mounted on the bed 10. At one end of the cylinder 150, there is provided an end plug 154 having an adjusting screw 155 therein for restricting the rightward movement of the piston 151. The limit of the rightward movement of the piston 151 may be adjusted by turning the adjusting screw 155.

A predetermined amount of pressure fluid is intermittently supplied from a hydraulic circuit of the grinding wheel head feed device 120 to the right chamber of the cylinder 150 on each stroke of the grinding wheel head 11, or upon the completion of a grinding operation of any one cam of the cam shaft, or workpiece W.

The compensating device for the advancing limit of the grinding wheel head 11 will be briefly described hereinafter.

Referring to FIG. 11, the cylinder 150 is connected to a first'change-over valve 200. A check valve 201 is provided in series between the cylinder 150 and the change-over valve 200. The reference numeral 202 indicates a cylinder for determining the compensating amount of the second stop member 140, and has a slidable piston 203 therein. The adjusting screw 204 is provided for determining the compensating amount. The right chamber of the cylinder 202 is connected to the right chamber of the cylinder 150 through a second change-over valve 205, which is hydraulically operated in response to the pressures in the left and right chambers of the cylinder 120, at the illustrated position in FIG. 11. The left chamber of the cylinder 202 is connected to the second change-over valve 205. The second change-over valve is connected to the cylinder 120 and a third change-over valve 206. The left chamber of the cylinder 120 is further connected through change-over valve 206 to a fourth change-over valve 207, which has a throttling effect on flow therethrough when the change-over valve 207 is actuated by a limit switch 178, presently to be described, for changing the feed speed rate of the grinding wheel head 11.

In the condition shown in FIG. 11, when pressurized fluid is supplied to the cylinder 120 through the third change-over valve 206, the second change-over valve 205 is changed to the opposite position so as to move the piston 203 of the cylinder 202. As a limit switch 178 is actuated after a predetermined advance of the grinding wheel head 11, the fourth change-over valve 207 is changed to the opposite position to decrease the feed speed of the grinding wheel head 11. At the advanced end of the movement of grinding wheel head 11, the third change-over valve 206 is actuated so that the piston of the cylinder 120 is moved now to the right. Simultaneously, the second change-over valve 205 is shifted back to the illustrated position of FIG. 11 so that the piston 203 of the cylinder 202 is also moved to the right. The fluid evacuated from the right chamber of the cylinder 202 is supplied to the cylinder 150 so that the piston 151 therein may be moved to the left, see FIG. 8, in accordance with the fluid volume from the cylinder 202, whereby the position of the second stop member 140 is adjusted to compensate for grinding wheel wear.

Thus, the shaft 144 is intermittently rotated through the mesh between the rack 153 and the pinion 147 in response to the intermittent leftward movement of the piston 151 so as to slightly downwardly move the plunger 142 through the threaded engagement between the shaft 144 and the plunger 142. Therefore, the forward end of the grinding wheel head 11 is moved slightly forward during each fine grinding operation, and it should be understood that variation of the finished dimensions of the workpiece W according to wear of the grinding wheel 12 maybe automatically compensated for, whereby the cams on the workpiece W may always be finished to the same desired dimensrons.

The aforementioned grinding feed device 120 for the grinding wheel head 11 is shown inFIG. 9 in detail, and comprises a cylinder 127 mounted on the bed and a piston 121 slidably mounted therein. The rack 123 is formed on a piston rod 122 of the piston 121 and engages the pinion 103 of the cylindrical member 102 so that the grinding wheel head 11 is automatically advanced in response to the leftward movement of the piston 121, as shown in FIG. 9, since the tapered contact surfaces 108a and 111a are frictionally engaged with each other. A shaft is threadedly engaged with a blocking member 124 attached to the right end of the cylinder 127. The left end of the shaft 125 abuts the right side of the piston 121 and serves as a stop member which is referred to as a third stop member 128 hereinafter. A pinion 126 formed on the other end of the shaft 125 meshes with a rack 163 formed on a piston rod 162. A piston 161 integrally carrying the piston rod 162 is slidably mounted in a cylinder also mounted on the bed 10. At the extending portion of the piston rod 162, there is provided a stop member 164 in the form of an adjusting screw. The stop member 164 is threadedly mounted on a bracket 165 secured on the bed 10 and serves to limit the upward movement of the piston 161. Accordingly, the end of the upward movement of thepiston 161 may be adjusted by turning the stop member 164.

When the piston 161 begins to move upwardly, the shaft 125 is rotated to cause the third stop member 128 to be moved to the left, as viewed in FIG. 9, so that it projects into the cylinder 127 a predetermined distance, through the mesh between the rack 163 and the pinion 126, until the piston 161 reaches its stroke end, or the top of the piston rod 162 abuts the stop member 164. Consequently, the effective stroke of the piston 121, or the extent of movement of the grinding wheel head 11 which is permitted, may be changed. In other words, in FIG. 9, as the leftward movement of the piston 121 causes the grinding wheel head 11 to advance and the rightward movement thereof causes the grinding wheel head 11 to retract, it should be understood that the limit of retraction of the grinding wheel head 11 may be changed to be near the point to which advancing movement thereof was limited in the rough grinding operation after completion of such rough grinding operations.

Accordingly, in operation, after all the cams of the workpiece W are rough ground, the above-mentioned first stop member 130 is deactuated by means of retracting the piston rod 134, and at this time the piston 161 is simultaneously moved upwardly to change the point to which the grinding wheel head 11 may now be retracted, and then the fine grinding operations are successively applied on the various cam portions of the workpiece W. This narrowing of the extent of the retracting stroke of the grinding wheel head 11 may be useful for eliminating idle grinding time. It is very difficult to completely eliminate idle grinding time, however, but by adjusting the position of the stop member 164 for changing the point to which the grinding wheel head 11 is retracted before fine grinding each cam, the above-mentioned idle grinding time may be minimized as much as possible.

Referring now to FIGS. 7, 8 and 10, a gear is fixedly mounted on the cylindrical member 102 adjacent the flange 105, being meshed with a gear 173 through a counter gear 171 which is rotatably mounted on the bed 10 through a counter shaft 184 and a supporting plate 186. The gear 173 is rotatably mounted on an adjusting shaft 172 which is rotatably mounted on the supporting plate 186 secured to the bed 10.

A gear 175 is also fixedly mounted on the adjusting shaft l72'adjacent the gear 173 and meshes with a gear 177 rotatably mounted on the bed 10 through a shaft and the supporting plate 186. The gear 177 carries a dog plate 176 for actuating a limit switch 178 also mounted on the bed 10. The limit switch 178 serves to change the feed speed rate of the grinding wheel head 1 l, or in other words, when the limit switch 178 is actuated, fluid flow rate from the cylinder 127 for feeding the grinding wheel head 11 is restricted or changed to a smaller amount.

A sleeve 181 is slidably mounted on the adjusting shaft 172 and is adapted to abut the gear 173 at one end thereof and at the other end carries an adjusting knob 180 having indicia thereon. The sleeve 181 can be rotated with the adjusting shaft 172 through a connecting pin 187 mounted thereon, A screw bolt 182 is threadedly engaged in one end of the adjusting shaft 172 through the adjusting knob 180. In this construction, when the screw bolt 182 is tightened by turning thereof, the sleeve 181 is moved toward the gear 173 so as to push the sleeve 181 against the gear 175 through the gear 173 therebetween to provide such frictional engagement that will permit the gear 173 to be rotated with the adjusting shaft 172.

Accordingly, the rotation of the gear 170 is transmitted to the dog plate 176 through the gears 171, 173, 175 and 177 to cause the limit switch 178 to be actuated. On the other hand, when the screw bolt 182 is loosened, the sleeve 181 is released from its frictional engagement with the gear 173, and the gear 173 cannot rotate with the adjusting shaft 172. Consequently, the rotation of the gear 170 may not be transmitted to the dog plate 176, but instead the gear 173 is turned freely on shaft 172. As the adjusting knob 180 can be freely rotated irrelevant of the gear 173 and as rotation of the adjusting knob 180 is only transmitted to the gear 177 through the shaft 172, and gear 175 thereon, the position of the dog plate 176 is easily adjusted by rotating the adjusting knob 180.

Now, hereinafter explained is the operation of the above-described grinding machine embodying the present invention.

The workpiece W, or the camshaft having a plurality of cams to be ground, is worked by two process steps, in the first process step all cam portions of the workpiece W being rough ground, and in the next second step, all cam portions thereof being fine ground.

Before beginning the first process step, the hydraulic actuators and other devices are prepared for a rough grinding operation. In other words, the first stop member 130 is actuated by shifting the piston 133 leftwardly, as viewed in FIG. 7, so as to limit advancement of the grinding wheel head 11 during any movement thereof in that direction, and the third stop member 128 is inactivated by retracting the piston 161. The position of the engaging pin 114 is adjusted to the proper position for limiting the retraction of the grinding wheel head 11. The position of the dog plate 176 with respect to the limit switch 178 is adjusted by loosening the bolt 182 and turning the adjusting knob 180 so that the limit switch is positioned for actuation just before the grinding wheel head 11 reaches its advancing limit, and afterward the bolt 182 is retightened. Accordingly, the limit switch 178 may be actuated shortly after beginning the fine grinding operation. In consequence, in fine grinding operations, the grinding wheel head 1 1 may be advanced toward the workpiece W at a feed speed which is just the same as the rough grinding feed speed, and after the grinding wheel 12 abuts with the workpiece W, the feed speed of the grinding wheel head 11 may be decreased by actuation of the limit switch 178.

The pistons 22 and 121 of the hydraulic actuators 21a and 120 are retracted to the original positions and the swing table 32 is also retracted by the downward movement of the piston 66 so that the master earns 35 are taken out of engagement with the cam roller 41. In this fashion, the unworked workpiece W may be mounted on the machine. Then the traverse table 28 is indexed so that a first cam portion to be ground on the workpiece W corresponds with the grinding wheel 12. At the same time, as the supporting member 40 is shifted in response to movement of the traverse table 28 through the rack 44, the gears 45, 48, and 47, and the engaging dog 49, the cam roller 41 may be indexed to the corresponding one of the master cams 35.

The pistons 61 are shifted up for increasing the contact pressure between the cam roller 41 and the master cam 35 and the piston 76 of the tail stock is also moved leftwardly for increasing the compression force of the work center 72.

Now, the piston 66 is moved upwardly so that the master cam 35 contacts the cam roller 41, and when the spindle 30 begins to rotate, the workpiece W also begins to rotate and to swingably move, whereafter the grinding wheel head 11 is advanced toward the workpiece W at a rapid feed speed by the action of the hydraulic actuator 21a until the forward end of the feed shaft 20a engages with the stop member 19 while the hydraulic actuator 120 is simultaneously actuated for feeding the grinding wheel head 11 through frictional engagement of the tapered contact surfaces 108a and 111a. Thus, a rough grinding operation is applied on the first cam portion of the workpiece W being ground until the projection 104 of the flange abuts the first stop member 130, or namely until the dimension of the workpiece W reaches a predetermined value. Then, the grinding wheel head 11 is retracted to its starting position at rapid feed speed after a predetermined sparkout operation.

The term spark-out operation as used herein may be defined as a stopping of the feed movement of a grinding wheel, while the grinding operation continues by virtue of permitting the workpiece to return to or assume its normal position after having been distorted by the grinding feed. The grinding operation stops entirely when the strain on the workpiece has been completely relieved due to the grinding away of the peripheral or other surface thereof.

Upon the retraction of the grinding wheel head 11, the traverse table 28 is indexed relative to the grinding wheel 12 to the next, or second, cam to be ground thereby, which is spaced from the first cam, already ground, and the cam roller 41 is also indexed to the next master cam 35. Thus, when the grinding wheel head 11 is advanced toward the second cam portion, the next rough grinding operation may be applied thereto, and in such a manner, the remaining cams of the workpiece W may be successively rough ground.

Upon the completion of the spark-out operation with the final cam being ground, the third stop member 128 is automatically actuated through actuation of the piston 161 for restricting the extent of retraction permitted of the grinding wheel head 11. In this fashion, the traverse table 28 is automatically shifted to the starting position where the first ground cam corresponds with the grinding wheel 12, and the respective hydraulic actuators and other devices are automatically changed so as to carry out the second step of the process, namely the fine grinding operation. In other words, the first stop member 130 is deactivated by retracting the piston 133, and it should be understood that in the fine grinding operation, the advancing limit of the grinding wheel head 11 is established by the second stop member 140. Thepistons 61 and piston 86 are moved to their respective opposite positions from the positions previously held thereby for decreasing the contact pressure between the cam roller 41 and the master cam 35 and the pushing force of the work center 72. The manner in which the hydraulic actuators are changed is well known in the art, and such operation may be realized by using conventional change-over valves and the like.

In this condition, fine grinding operations may be successively performed on the cams of the workpiece W. The grinding wheel head 11 is advanced toward the first cam at a rapid feed speed by the action of the hydraulic actuator 21a until just before the grinding wheel 12 contacts the first cam portion, and then the grinding wheel head 11 is advanced at a slow feed speed, which is the same as that of the rough grinding feed speed. Therefore, the cam portion of the workpiece is ground at the rough grinding feed speed for a short while until the limit switch 178 is actuated by engagement thereof with the dog plate 176, which causes the grinding wheel head feed speed to further decrease because the fluid flow rate from the cylinder 127 is decreased in a well known method. Consequently, the first cam may be ground at a decreased or fine feed speed. When the dimension of the cam portion being ground reaches its predetermined desired figure, the grinding wheel head 11 is retracted to the new starting position, previously established as indicated hereinabove by the stop 128, after a predetermined spark-out operation. Similarly, the second cam may be fine ground, and in the same manner, the remaining cams may be successively fine ground until all grinding operations are completed.

The grinding wheel 12 may be dressed by the dressing device 90 after all cams of the workpiece W have been rough ground, this dressing operation being applied on the grinding wheel 12 during any rough or fine grinding operation, and as it is not necessary to apply a dressing operation for each cam, several cams may be ground between dressing operations. Furthermore, the dressing speed may be automatically changed according to the grinding condition and the position of the grinding wheel head 11 with respect to the workpiece W may be simultaneously compensated.

It should now be apparent that the present invention relates to an improved grinding machine wherein a workpiece having a plurality of portions thereon to be ground is effectively ground, and wear of the grinding wheel is greatly decreased. In addition, the grinding machine according to the present invention provides improved accuracy in the finished workpiece in comparison with a workpiece which has been worked by performing rough and fine grinding operations alternatively on the various portions being ground. Furthermore, as the starting position of the grinding wheel head is changed to be near the end of advancement thereof as made during the rough grinding operation, when the fine grinding operation is begun, idle grinding time is substantially eliminated, whereby grinding efficiency is improved.

While the invention has been described by means of a specific embodiment, it should be understood that the novel characteristics of the invention may be incorporated in other structural forms without departing from the spirit and scope of the invention as defined in the following claims.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

l. A grinding machine for grinding a workpiece having a plurality of portions to be ground, comprising:

a bed; i

a grinding wheel head slidably mounted on said bed and rotatably supporting a grinding wheel;

a traverse table slidably mounted on said bed and having a head stock and a tail stock thereon for rotatably supporting a workpiece therebetween;

an indexing means mounted on said bed being operatively engaged with said traverse table for indexing one of said grinding portions on said workpiece with respect to said grinding wheel;

a feed mechanism mounted on said bed being operatively connected to said grinding wheel head for advancing and retracting said grinding wheel head relative to said workpiece;

a first stop member mounted on said bed for engaging said feed mechanism for limiting the advance of said grinding wheel head during rough grinding operations;

a second stop member mounted on said bed for engaging said feed mechanism for limiting the advance of said grinding wheel head during fine grinding operations; and,

a change-over valve hydraulically connected to said first stop member for deactuating the same in response to the completion of rough grinding operations being applied on all of said portions being ground.

2. A grinding machine as set forth in claim 1, wherein said first stop member comprises a cylinder mounted on said bed and a piston slidably mounted in said cylinder having a piston rod thereon;

said piston rod serving as a stop member for mechanically engaging an engaging portion provided on said grinding wheel head feed mechanism during advancement thereof, whereby said advan'cement of said grinding wheel head is limited by said first stop member during rough grinding operations.

3. A grinding machine as set forth in claim 1, wherein said second stop member comprises a supporting block mounted on said bed and a plunger axially adjustable therein;

said plunger having an inclined fiat surface thereon and being opposite an engaging portion on said grinding wheel head feed mechanism for engaging the same during advancement of said grinding wheel head, whereby said advancement of said grinding wheel head is limited by said second stop member during fine grinding operations.

4. A grinding machine as set forth in claim 3, wherein said second stop member further comprises a cylinder mounted on said bed and a piston slidably mounted therein;

a piston rod of said piston being provided with a rack portion which is mechanically connected to said plunger, whereby said plunger is axially movable in said supporting block in response to movement of said piston for changing the limiting point to which said grinding wheel head may be advanced.

5. A grinding machine as set forth in claim 4, wherein said cylinder of said second stop member is connected to means for compensating the advancement of said grinding wheel head for wear,

said compensating means comprises a cylinder connected to said second stop member and said feed mechanism for determining the compensating amount of said second stop member, and a main change-over valve provided between said lastnamed cylinder and said feed mechanism for sending a predetermined amount of fluid in said lastnamed cylinder to said cylinder of said second stop member in response to each reciprocation of said grinding wheel head.

6. A grinding machine as set forth in claim 1, wherein said feed mechanism for said grinding wheel head comprises a first hydraulic actuator mounted on said bed being mechanically connected to said grinding wheel head for reciprocably moving the same with respect to said workpiece at a rapid feed speed;

a second hydraulic actuator mounted on said bed being operatively connected to said grinding wheel head for reciprocably moving the same with respect to said workpiece at a grinding feed speed; and,

a third stop member provided in said second hydraulic actuator being operable after said plurality of portions are rough ground for limiting the extent of retraction of said grinding wheel head.

7. A grinding machine as set forth in claim 6, wherein said second hydraulic actuator comprises a second cylinder and a second piston, and

said third stop member comprises a shaft threadedly engaged with one end of said second cylinder being adapted to abut said second piston at one end thereof and having a pinion at the other end thereof; and further comprising:

a third hydraulic actuator including a third cylinder mounted on said bed and having a third piston slidably mounted therein,

a piston rod of said third piston being provided with a rack which engages said pinion, whereby said shaft is movable into and out said cylinder in response to the movement of said third hydraulic actuator for limiting the extent of retraction of said grinding wheel head during fine grinding operations.

8. A grinding machine as set forth in claim 1, wherein said tail stock comprises a sleeve slidably mounted in a body thereof having a work center;

a cylinder having a piston slidably mounted therein;

said cylinder and piston being coaxially aligned with said work center; and,

a spring inserted between said sleeve and said piston for urging said workpiece in one direction,

whereby compression of said spring is changed by supply and exhaust of pressure fluid into said cylinder.

9. A cam grinding machine comprising:

a bed;

a traverse table slidably mounted on said bed;

a swing table pivotably mounted on said traverse table;

a head stock and a tail stock mounted on said swing table for rotatably supporting a workpiece having a plurality of portions to be ground;

a grinding wheel head slidably mounted on said bed and rotatably supporting a grinding wheel;

a plurality of master cams rotatably mounted on said swing table;

a cam roller rotatably mounted on said head stock;

means for urging said master cams toward said cam roller for making engagement between said cam roller and a selected one of said master earns;

a feed mechanism mounted on said bed and operatively connected to said grinding wheel head for advancing and retracting the same relative to said workpiece;

first stop member mounted on said bed and adapted to be engaged by said feed mechanism for limiting advancement of said grinding wheel head during rough grinding operations;

second stop member mounted on said bed and adapted to be engaged by said feed mechanism for limiting advancement of said grinding wheel head during fine grinding operations;

third stop member provided in said feed mechanism for limiting the extent of retraction of said grinding wheel head during fine grinding operations; and,

means for deactuating said first stop member and for actuating said third stop member in response to the completion of rough grinding operations performed on said plurality of workpiece portions.

10. A cam grinding machine as set forth in claim 9, wherein said first stop member comprises a cylinder mounted on said bed; and,

a piston slidably mounted in said cylinder having a piston rod thereon;

said piston rod serving as a stop member mechanically engaging an engaging portion provided on said grinding wheel head feed mechanism at the forward end of said advancement of said grinding wheel head.

11. A cam grinding machine as set forth in claim 9, wherein said second stop member comprises a supporting block mounted in said bed and a plunger being axially adjustable in said supporting block;

said plunger having an inclined flat surface thereon and being oppositely disposed of an engaging portion on said grinding wheel head feed mechanism for engagement therewith when said grinding wheel head is being advanced.

12. A cam grinding machine as set forth in claim 11, wherein said second stop member further comprises a cylinder mounted on said bed and a piston slidably mounted therein;

a piston rod of said piston being provided with a rack portion which is mechanically connected to said plunger, whereby said plunger is axially moved responsive to the movement of said piston so as to 1 change the forward end of advancement of said grinding wheel head.

13. A cam grinding machine as set forth in claim 9, wherein said feed mechanism comprises a cylinder and a piston slidably received therein; and,

wherein said third stop member comprises a shaft member threadedly engaged with said cylinder and adapted to abut said piston; and further comprising:

means connected to said shaft member for moving said shaft member toward and from said piston.

14. A cam grinding machine as set forth in claim 9,

wherein said urging means comprises:

having a plurality of portions to be ground, comprising:

a bed; a grinding wheel head slidably mounted on said bed I and rotatably supporting a grinding wheel; a traverse table slidably mounted on said bed and having a head stock and a tail stock thereon for rotatably supporting said workpiece therebetween; means for indexing said traverse table for positioning said workpiece portions selectively before said grinding wheel;

a feed mechanism for advancing said grinding wheel head toward said workpiece and retracting the same therefrom;

means for limiting the advancement of said grinding wheel head during rough grinding operations;

means for limiting the advancement of said grinding v wheel head during fine grinding operations; and,

means for limiting the retraction of said grinding wheel head during fine grinding operations to a point near the rough grinding advancing limit thereof.

16. A grinding machine as set forth in claim 15, further comprising means connected with said feed mechanism and said fine grinding advancement limiting means for changing the advancement of said grinding wheel head permitted thereby to compensate for grinding wheel wear. 

1. A grinding machine for grinding a workpiece having a plurality of portions to be ground, comprising: a bed; a grinding wheel head slidably mounted on said bed and rotatably supporting a grinding wheel; a traverse table slidably mounted on said bed and having a head stock and a tail stock thereon for rotatably supporting a workpiece therebetween; an indexing means mounted on said bed being operatively engaged with said traverse table for indexing one of said grinding portions on said workpiece with respect to said grinding wheel; a feed mechanism mounted on said bed being operatively connected to said grinding wheel head for advancing and retracting said grinding wheel head relative to said workpiece; a first stop member mounted on said bed for engaging said feed mechanism for limiting the advance of said grinding wheel head during rough grinding operations; a second stop member mounted on said bed for engaging said feed mechanism for limiting the advance of said grinding wheel head during fine grinding operations; and, a change-over valve hydraulically connected to said first stop member for deactuating the same in response to the completion of rough grinding operations being applied on all of said portions being ground.
 2. A grinding machine as set forth in claim 1, wherein said first stop member comprises a cylinder mounted on said bed and a piston slidably mounted in said cylinder having a piston rod thereon; said piston rod serving as a stop member for mechanically engaging an engaging portion provided on said grinding wheel head feed mechanism during advancement thereof, whereby said advancement of said grinding wheel head is limited by said first stop member during rough grinding operations.
 3. A grinding machine as set forth in claim 1, wherein said second stop member comprises a supporting block mounted on said bed and a plunger axially adjustable therein; said plunger having an inclined flat surface thereon and being opposite an engaging portion on said grinding wheel head feed mechanism for engaging the same during advancement of said grinding wheel head, whereby said advancement of said grinding wheel head is limited by said second stop member during fine grinding operations.
 4. A grinding machine as set forth in claim 3, wherein said second stop member further comprises a cylinder mounted on said bed and a piston slidably mounted therein; a piston rod of said piston being provided with a rack portion which is mechanically connected to said plunger, whereby said plunger is axially movable in said supportiNg block in response to movement of said piston for changing the limiting point to which said grinding wheel head may be advanced.
 5. A grinding machine as set forth in claim 4, wherein said cylinder of said second stop member is connected to means for compensating the advancement of said grinding wheel head for wear, said compensating means comprises a cylinder connected to said second stop member and said feed mechanism for determining the compensating amount of said second stop member, and a main change-over valve provided between said last-named cylinder and said feed mechanism for sending a predetermined amount of fluid in said last-named cylinder to said cylinder of said second stop member in response to each reciprocation of said grinding wheel head.
 6. A grinding machine as set forth in claim 1, wherein said feed mechanism for said grinding wheel head comprises a first hydraulic actuator mounted on said bed being mechanically connected to said grinding wheel head for reciprocably moving the same with respect to said workpiece at a rapid feed speed; a second hydraulic actuator mounted on said bed being operatively connected to said grinding wheel head for reciprocably moving the same with respect to said workpiece at a grinding feed speed; and, a third stop member provided in said second hydraulic actuator being operable after said plurality of portions are rough ground for limiting the extent of retraction of said grinding wheel head.
 7. A grinding machine as set forth in claim 6, wherein said second hydraulic actuator comprises a second cylinder and a second piston, and said third stop member comprises a shaft threadedly engaged with one end of said second cylinder being adapted to abut said second piston at one end thereof and having a pinion at the other end thereof; and further comprising: a third hydraulic actuator including a third cylinder mounted on said bed and having a third piston slidably mounted therein, a piston rod of said third piston being provided with a rack which engages said pinion, whereby said shaft is movable into and out said cylinder in response to the movement of said third hydraulic actuator for limiting the extent of retraction of said grinding wheel head during fine grinding operations.
 8. A grinding machine as set forth in claim 1, wherein said tail stock comprises a sleeve slidably mounted in a body thereof having a work center; a cylinder having a piston slidably mounted therein; said cylinder and piston being coaxially aligned with said work center; and, a spring inserted between said sleeve and said piston for urging said workpiece in one direction, whereby compression of said spring is changed by supply and exhaust of pressure fluid into said cylinder.
 9. A cam grinding machine comprising: a bed; a traverse table slidably mounted on said bed; a swing table pivotably mounted on said traverse table; a head stock and a tail stock mounted on said swing table for rotatably supporting a workpiece having a plurality of portions to be ground; a grinding wheel head slidably mounted on said bed and rotatably supporting a grinding wheel; a plurality of master cams rotatably mounted on said swing table; a cam roller rotatably mounted on said head stock; means for urging said master cams toward said cam roller for making engagement between said cam roller and a selected one of said master cams; a feed mechanism mounted on said bed and operatively connected to said grinding wheel head for advancing and retracting the same relative to said workpiece; a first stop member mounted on said bed and adapted to be engaged by said feed mechanism for limiting advancement of said grinding wheel head during rough grinding operations; a second stop member mounted on said bed and adapted to be engaged by said feed mechanism for limiting advancement of said grinding wheel head during fine grinding operations; a third stop member proVided in said feed mechanism for limiting the extent of retraction of said grinding wheel head during fine grinding operations; and, means for deactuating said first stop member and for actuating said third stop member in response to the completion of rough grinding operations performed on said plurality of workpiece portions.
 10. A cam grinding machine as set forth in claim 9, wherein said first stop member comprises a cylinder mounted on said bed; and, a piston slidably mounted in said cylinder having a piston rod thereon; said piston rod serving as a stop member mechanically engaging an engaging portion provided on said grinding wheel head feed mechanism at the forward end of said advancement of said grinding wheel head.
 11. A cam grinding machine as set forth in claim 9, wherein said second stop member comprises a supporting block mounted in said bed and a plunger being axially adjustable in said supporting block; said plunger having an inclined flat surface thereon and being oppositely disposed of an engaging portion on said grinding wheel head feed mechanism for engagement therewith when said grinding wheel head is being advanced.
 12. A cam grinding machine as set forth in claim 11, wherein said second stop member further comprises a cylinder mounted on said bed and a piston slidably mounted therein; a piston rod of said piston being provided with a rack portion which is mechanically connected to said plunger, whereby said plunger is axially moved responsive to the movement of said piston so as to change the forward end of advancement of said grinding wheel head.
 13. A cam grinding machine as set forth in claim 9, wherein said feed mechanism comprises a cylinder and a piston slidably received therein; and, wherein said third stop member comprises a shaft member threadedly engaged with said cylinder and adapted to abut said piston; and further comprising: means connected to said shaft member for moving said shaft member toward and from said piston.
 14. A cam grinding machine as set forth in claim 9, wherein said urging means comprises: a cylinder provided on said head stock; a piston slidably received in said cylinder; a sleeve adjustably mounted in said piston; resilient means provided between said sleeve and said swing table; whereby the tension of said resilient means is changed by supply of pressure fluid into said cylinder.
 15. A grinding machine for grinding a workpiece having a plurality of portions to be ground, comprising: a bed; a grinding wheel head slidably mounted on said bed and rotatably supporting a grinding wheel; a traverse table slidably mounted on said bed and having a head stock and a tail stock thereon for rotatably supporting said workpiece therebetween; means for indexing said traverse table for positioning said workpiece portions selectively before said grinding wheel; a feed mechanism for advancing said grinding wheel head toward said workpiece and retracting the same therefrom; means for limiting the advancement of said grinding wheel head during rough grinding operations; means for limiting the advancement of said grinding wheel head during fine grinding operations; and, means for limiting the retraction of said grinding wheel head during fine grinding operations to a point near the rough grinding advancing limit thereof.
 16. A grinding machine as set forth in claim 15, further comprising means connected with said feed mechanism and said fine grinding advancement limiting means for changing the advancement of said grinding wheel head permitted thereby to compensate for grinding wheel wear. 